Safety mechanism for power-operated presses and the like



Dec. 30, 1969 L. F. GRUNDY 3,487,182

SAFETY MECHANISM FOR POWER-OPERATED PRESSES AND THE LIKE Filed Feb. 6,1969 4 Sheets-Sheet 1 AT TORNEYS I... F. GRUNDY Dec. 30, 1969 4Sheets-Sheet 2 Filed Feb. 6, 1969 FIQZ INVENTOR LAWRENCE E GRUNDY LLb-AT TORNEYS Dec. 30, 1969 L. F. GRUNDY 3,487,182

SAFETY MECHANISM FOR POWER-OPERATED PRESSES AND THE LIKE Filed Feb 6,1969 4 Sheets-Sheet 5 IN VENTOF? LAWRENCE E GRUNDY AT TORNEYS Dec. 30,1969 L. F. GRUNDY 3,487,182

SAFETY MECHANISM FOR POWER-OPERATED PRESSES AND THE LIKE Filed Feb. 6,1969 4 Sheets-Sheet 4 I 35 B7 25 if 40 ij Q c 1 1,

IN VENTOR LAWRENCE E GRUNDY AT TORNEYS United States Patent 3,487,182SAFETY MECHANISM FOR POWER-OPERATED PRESSES AND THE LIKE Lawrence F.Grundy, Kirtland, Ohio, assignor to The Positive Safety ManufacturingCompany, Cleveland, Ohio, a corporation of Ohio Filed Feb. 6, 1969, Ser.No. 797,207 Int. Cl. H0lh 3/16 US. Cl. ZOO-61.42 Claims ABSTRACT OF THEDISCLOSURE A safety mechanism is provided for preventing actuation ofthe press ram in the event there is an obstruction in the work area ofthe press. The mechanism is characterized by the fact that it embodies asolenoid and senser mechanism responsive to energization of thesolenoid, but which senser mechanism falls by gravity. Additionalfeatures include the use of a relay and limit switch, means forimproving controlled movement of the senser, means for preventingmisalignment or distortion of parts of the senser mechanism, and meansfor reducing friction at various points in the mechanism.

This invention relates, as indicated, to a safety mechanism, which isespecially useful in the operation of small presses, such, for example,as used for riveting, staking, and the like.

In Cain Patent 3,315,049, a safety switch means for a machine having apower-stroking operation is disclosed, including a senser which ismovable to a location opera tively in the path of a power ram of themachine, a con trol rod for movably supporting the senser, a solenoidfor moving the control rod, and thus also the senser to said location(the senser being of a nature to detect an obstruction if existing alongsaid path, so that the movement of the senser into said location assuresthat said path is free from obstruction), safety switches for energizingsaid solenoid, and an abutment on the control rod for actuating anormally-open switch which controls the movement of the ram, butoperable only upon the senser having reached said location, assuringthat the opera tional effect cannot be actuated if there is anyobstruction preventing the senser from having reached said location.

In said Cain patent, the abutment on the control rod is adjustable alongthe control rod, as is the senser, and a compression coil spring isprovided which holds the rod upwardly except when the solenoid isenergized, the tension of this coil spring being also adjustable.

It has been found, in utilizing the safety switch means of the aforesaidpatent, that there are certain disadvantages in the arrangementdescribed in the patent, which maybe enumerated as follows:

(1) When working on sensitive material, the force of the senser beingdriven against an object by the solenoid may be sufficient to damage thematerial or compress the finger or fingers of the hand to a point atwhich the normally-open switch may be inadvertently closed, and the ramthus inadvertently operated.

(2) In order to achieve a desired easy working of the system, thesolenoid has to be custom-designed, at a cost which is almostprohibitive, since it is difficult to find commercially availablesolenoids having operating characteristics necessary for the purposes ofthe invention described in the Cain patent.

(3) The mass or weight of the senser mechanism is so great, and thereturn coil spring is so strong, that the force of the solenoid requiredto overcome this weight and strength results in greater pressure on thesenser than is desirable.

3,487,182 Patented Dec. 30, 1969 (4) No provision is made in the Cainpatent for preventing misalignment or distortion of the control rod.

We have developed a safety switch system which has numerous advantagesover that described in the Cain patent, including among others, thefollowing:

1) The force required to operate or actuate the senser or sensormechanism is considerably smaller.

(2) Means are provided which slow down the operation sufficiently toprovide better control of the senser.

(3) By eliminating a driven senser, and utilizing a gravity-actuatedsenser, in which pivotal connection between components are utilized,very little wear is effected at pivot points in the system.

(4) Commercially available solenoids, purchasable at low cost, can beused.

(5) Means have been provided for preventing or minimizing misalignmentand distortion of the senser controd rod and senser.

(6) A relay is used, which prevents actuation of the machine by manuallyoperating the senser.

(7) An adjusting collar is provided which limits the return movement ofthe senser control rod, and, at the same time, provides a means ofadjusting the stroke of the senser.

(8) The senser control rod is independently adjustable, that is to say,it is infinitely adjustable.

Other objects and advantages of my invention will be apparent during thecourse of the following description.

In the accompanying drawings forming a part of this specification, likenumerals are employed to designate like parts throughout the same.

FIG. 1 is a fragmentary perspective view of a press or press deviceembodying the safety means of the present invention, but with the coverof the safety means removed to more clearly show details thereof;

FIG. 2 is a fragmentary cross-sectional view, taken on the line 2-2 ofFIG. 1;

FIG. 3 is a fragmentary elevational view, as seen in the directionindicated by the arrows 3-3 of FIG. 1;

FIG. 4 is a fragmentary cross-sectional view, taken on the line 4-4 ofFIG. 3, and

FIG. 5 is a wiring diagram of the safety means, and circuitry therefor.

Referring more particularly to the drawings, there is illustrated apress 1, shown diagrammatically as having a base or bed 2 having anupright supporting column 3, which carries a fixed press-head 4. Fromthe head 4, there extends downwardly an axially-movable power ram orpunch 5 designed to coact with work-holding means 6, which is secured tothe bed 2 in any suitable manner.

Electric power for actuation of the ram 5 is provided by an externaltwo-wire or three-wire electric supply 7 (see FIG. 5), as required byelectrical codes.

Normally open foot or hand switches 8 and 9', are provided in theelectric supply circuit, for the purpose of actuating the safety means,which then provides a source of power to the ram 5. In other cases,these would control a source of power for, or actuation of the ram.

The components thus described form no part of the present invention,except in their relation to and their cooperation with the safety meansof the invention.

In accordance with the invention, there is provided a senser or probecomprising a vertical rod 10 and a member extending angularly to the rod10 and terminating in a loop 11. This senser is caused to feel or testthe work area prior to any possibility of actuation of the ram 5; andonly if the work area is operationally free of any foreign object canthe senser cause the ram to be actuated. This action is subject toproper adjustment of the safety means, which adjustment will bepresently described.

The senser 11 is shown, in this instance, as in the shape of a loop, theaxis of which is coaxial with the axis of travel of the ram 5, and therod is adjustably secured in an actuator block 12, by means of a setscrew 12a.

The block 12 is secured, as by means of a hollow head screw 13, to asenser control rod or shaft 14, having a flattened area 15, againstwhich the stem of the screw 13 bears, to preclude rotation of the shaft14 in the block 12.

The shaft 14 is mounted for reciprocal slidable movement in a pair ofvertically-spaced bearing blocks 16 and 17 which are secured to a baseplate 18.

The block 16 has secured thereon, as by a screw 18a, a leaf spring 1811,to the upper end of which is secured, as by a screw 180, a drag block18d. This block bears resiliently and frictionally against the shaft 14and thus acts to slow the movement of the shaft sufiiciently to providebetter control of the senser. This drag block, in conjunction with alatch spring to be presently described, functions to provide suchimproved control of the senser.

The base plate 18 forms the base or back of a housing which is mountedon the head 4 of the press, as shown in FIG. 1, the cover of thishousing being omitted in FIG. 1, for purposes of clarity. The base plate18 has mounted thereon all of the elements comprising the safety meansof the invention.

The shaft 14 has adjustably secured thereto, as by means of a screw 19,a collar 20, on which is superimposed a rubber bumper 20a, which isdesigned to engage the lower surface of the bearing block 16 to therebylimit the upward movement of the shaft 14. This rubber bumper preventsmetal to metal contact between the collar and bearing block, in additionto its normal shockreducing function.

Secured to the actuator block 12, as by means of screws 21 and 22, is aswitch actuator 23, which is designed to engage a switch closing arm 24of a limit switch 24a, when the shaft 14 descends. The limit switch 24ais mounted on the base plate 18, in spaced relation to such plate.

The safety means further includes a solenoid 25 which is mounted on thebase plate 18, and the armature of which is designated by referencenumeral 26. The lower end of the armature 26 is secured, as by a pivotpin 27, to the arms of a spring yoke 28, so that the yoke has a slightdegree of pivotal movement relatively to the armature. Mounted on thepivot pin 27, between the arms of the yoke 28 is a roller 27a (see FIG.4), which serves a purpose to be presently described.

The lower end of the yoke 28 is secured to one end of a coil spring 29,the lower end of which is secured, as by a screw 30, to a post 31, whichis mounted on the base plate 18.

The upper end of the shaft 14 is provided with a pin 32 which extendsthrough a slide or bearing block 32a (FIG. 4), which, in turn, ismounted for slidable movement in a slot 33, at the rear of a pivot beam34. The beam 34 is mounted for pivotal movement on a post 35, which ismounted on the base plate 18.

The beam 34 has mounted thereon adjacent its forward end, a latch spring34a (FIG. 4), which, when the beam 34 is rotated in a clockwisedirection, as viewed in FIG. 4, resiliently embraces the roller 27a, tothereby provide improved control of the action of the senser.

The safety means further includes a relay 36, which is supported by abracket 36a, which is attached to the base! plate 18.

A terminal block 37 is also provided, which is secured to the base plate18 by means of screws 37a, and is provided with bridged terminals A, B,C and D.

Reference to the wiring diagram of FIG. 5 shows that the switches 8 and9 are respectively secured, as by wires 38 and 39, to the terminals Aand B of the terminal block 37, and that these terminals are secured, asby wires 40 and 41, to the solenoid 25.

The wires 40 and 41 are secured, as by Wi$ 42 and 43, to the relay 36.

The relay 36 is also provided with normally open contacts 44 and 45,which are connected, through the limit switch 24a, to the terminals Cand D of the terminal block 37, these terminals being connected, throughthe wires 46 and 47, to the machine or press control unit 48 whichcontrols the action of the ram 5. This control unit 48 is illustrateddiagrammatically, and might be a solenoid clutch actuator, a solenoidvalve (either pneumatically or hydraulically operated), or, in the caseof a solenoidactuated press, would be a solenoid winding or control.

The use and operation of the safety means may now be described asfollows:

With the ram or punch 5 in the elevated position, and the senser 11 inthe position shown in FIG. 1, the various parts of the safety means willbe disposed in the position shown in this figure.

When the operator closes the switches 8 and 9, the solenoid 25 and therelay 36 are activated, permitting the shaft 14 and senser 10-11 to bereleased and to descend by gravity. The senser weighs only a few ouncesand the drop is controlled to prevent discomfort to the fingers of theoperator should they be in the path of the senser.

If the senser is obstructed by an object, such as a finger of theoperator or a misplaced part, and thus is not permitted to complete itsfull travel, the control circuit (FIG. 5) remains open and the punch orram 5 will not be activated. This results from the fact that the limitswitch 24a cannot close, due to such obstruction, and the portion of thecircuit which is controlled by the limit switch 24a and relay 36 is notenergized.

If the senser encounters no obstacle and is permitted to travel itscomplete pre-selected distance, the circuit controlled by the limitswitch 24a and relay 36 is completed, and the ram or punch 5 isactivated. The control relay 36 is used to prevent the operator fromcycling the machine by hand by pulling the senser down manually.

The vertical position of the senser is adjustable to compensate fordifferences such as material thickness and height of the dies. Thisadjustment for height and stroke is permitted by means of the set screws12a and 19.

Upon completion of the downstroke of the ram or punch, the coil spring29 contracts, thereby returning the senser 10-11 to its initial positionpreparatory to another cycle of operation of the press.

Since the senser mechanism falls by gravity, the force required tooperate or actuate the senser mechanism is considerably smaller thanthat required to operate the corresponding mechanism in the aforesaidCain patent.

The provision of the drag block 18d and the latch spring 341: slows themovement of the shaft 14 sufiiciently to provide better control of thesenser.

Since the force required to operate or actuate the senser mechanism isconsiderably smaller than that required to operate or actuate thecorresponding mechanism in the aforesaid Cain patent, it is notnecessary to utilize expensive, custom-designed, armatures for use inthe present mechanism, and it is possible to use, instead, low-cost,commercially available or standard solenoids.

The use of the bearing blocks 16 and 17 and actuator block 12, as wellas the manner in which these are associated with the shaft 14 and senserrod 11, insures against misalignment and distortion of the senser rodand the senser loop.

The use of the relay prevents the operator from cycling or operating thepress by manually-actuated means, such as the hands of the operator, ora manually-controlled switch.

The use of the collar 20 is advantageous in that it provides anadjustable means of limiting the return movement of the shaft 14.

The senser is independently and infinitely adjustable.

Wear of the mechanism is reduced to a minimum, since there are only twopivotal connections employed,

and the pivotal movement between the pivotally-connected parts isrelatively slight.

Friction is reduced by reason of the rolling contact between the pivotbeam and the roller 27a. The sliding block 32a provides a bearing with aminimum amount of free movement. This reduces the total amount ofbacklash in the shaft 14 and the senser or probe assembly, andcontrolling the senser assembly produces a more positive actuation ofthe limit switch.

It is to be understood that the form of my invention, herewith shown anddescribed, is to be taken as a preferred example of the same, and thatvarious changes may be made in the shape, size and arrangement of partsthereof, without departing from the spirit of the invention or the scopeof the subjoined claims.

Having thus described my invention, I claim:

1. Safety means for a machine having an operational eflFect along apath, said safety means comprising senser means operatively movable to alocation in said path, movable support means movably supporting saidsenser means, said support means and said senser means being movable bygravity into said location, control means for actuating the power strokeof the machine, said senser means being responsive to the presence of anobstruction in said path to prevent actuation of said control means, thecontrol means being cooperative with said movable support means to beactuatable to energize said operational effect only if said senser meanshas reached said location without sensing any such obstruction,solenoidactuated means, and means connected to said support means andresponsive to selective operation of said solenoid actuated means formoving said support means and said senser means to their uppermostposition and for releasing these means from said position to fall bygravity to said location.

2. Safety means, as defined in claim 1, including springactuated meansoperative in opposition to said solenoidactuated means for returningsaid support means and senser means to their uppermost position, whensaid solenoid-actuated means is not energized.

3. Safety means, as defined in claim 2, including relay means fordelaying the actuation of said control means.

4. In a safety device of the character described, a base plate, acontrol shaft mounted on said base plate for slidable movement, a sensersupported by said control shaft, a limit switch, means connected to saidcontrol shaft for closing said limit switch upon reaching a limitposition, said shaft and senser being entirely movable downwardly bygravity, and means releasably holding and preventing said gravitymovement of said shaft and senser.

5. A safety device, as defined in claim 4, wherein said last-named meanscomprises an armature, a yoke secured to said armature, and a spring forpulling said yoke downwardly.

6. A safety device, as defined in claim 5, wherein a relay is providedin association with said limit switch for controlling the effect of saidswitch.

7. In a safety device of the character described, a base plate,vertically-spaced bearing blocks mounted on said base plate, a shaftmounted for reciprocal sliding movement in said bearing blocks, anactuator block adjustbly secured to said shaft, a senser carried by saidblock, a limit switch mounted on said base plate, means mounted on saidactuator block for closing said limit switch, and spring-actuated meansincluding means for releasably holding said shaft and senser in anelevated position to prevent free falling of said shaft through saidbearing blocks.

8. A safety device, as defined in claim 7, wherein said last mentionedmeans includes a beam pivotally mounted on said base plate and pivotallyconnected to said shaft, said beam bearing against said spring-actuatedmeans.

9. A safety device, as defined in claim 8, wherein said pivot beam has aslot in one end thereof, a slide block is mounted for slidable movementin said slot, and a pivot pin is provided which extends through saidblock.

10. A safety device, as defined in claim 9, wherein a drag block ismounted on one of said bearing blocks, said block being in frictionalcontact with said shaft, and a latch spring is mounted on said beam forengagement with said spring-actuated means.

References Cited FOREIGN PATENTS 731,051 6/1955 Great Britain.

ROBERT K. SCHAEFER, Primary Examiner M. GINSBURG, Assistant Examiner US.Cl. X.R. 192-134

